Comparing approaches to optimize cut-off scores for short cognitive screening instruments in mild cognitive impairment and dementia

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O'Caoimh, Rónán
Gao, Yang
Svendovski, Anton
Gallagher, Paul F.
Eustace, Joseph A.
Molloy, D. William
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Background: Although required to improve the usability of cognitive screening instruments (CSIs), the use of cut-off scores is controversial yet poorly researched. Objective: To explore cut-off scores for two short CSIs: the Standardized Mini-Mental State Examination (SMMSE) and Quick Mild Cognitive Impairment (Qmci) screen, describing adjustments in scores for diagnosis (MCI or dementia), age (<=, > 75 years), and education (<, >= 12 years), comparing two methods: the maximal accuracy approach, derived from receiver operating characteristic curves, and Youden's Index. Methods: Pooled analysis of assessments from patients attending memory clinics in Canada between 1999-2010 : 766 with mild cognitive impairment (MCI) and 1,746 with dementia, and 875 normal controls. Results: The Qmci was more accurate than the SMMSE in differentiating controls from MCI or cognitive impairment (MCI and dementia). Employing the maximal accuracy approach, the optimal SMMSE cut-off for cognitive impairment was < 28/30 (AUC 0.86, sensitivity 74%, specificity 88%) versus < 63/100 for the Qmci (AUC 0.93, sensitivity 85%, specificity 85%). Using Youden's Index, the optimal SMMSE cut-off remained < 28/30 but fell slightly to < 62/100 for the Qmci (sensitivity 83%, specificity 87%). The optimal cut-off for MCI was < 29/30 for the SMMSE and < 67/100 for the Qmci, irrespective of technique. The maximal accuracy approach generally produced higher Qmci cut-offs than Youden's Index, both requiring adjustment for age and education. There were no clinically meaningful differences in SMMSE cut- off scores by age and education or method employed. Conclusion: Caution should be exercised selecting cut-offs as these differ by age, education, and method of derivation, with the extent of adjustment varying between CSIs.
Cognitive screening , Cut-offs , Dementia , Mild cognitive impairment , Quick mild cognitive impairment screen , Standardized mini-mental state examination
O’Caoimh, R., Gao, Y., Svendovski, A., Gallagher, P., Eustace, J. and Molloy, D. W. (2017) 'Comparing approaches to optimize cut-off scores for short cognitive screening instruments in mild cognitive impairment and dementia', Journal of Alzheimer's Disease, 57, pp. 123-133. doi: 10.3233/JAD-161204